As reported on the CNN website, the water in a small Colorado town has tested positive for tetrahydrocannabinol, the active ingredient in marijuana.
Hugo, the town in question, does not have either medical or recreational marijuana facilities. The source of contamination, and whether or not it was a deliberate act, is still under investigation by local and federal authorities.
According to CNN:
Signs of tampering were found on one of the five main wells that supplies water to the town of 720 people about 100 miles southeast of Denver... The contaminated well has been closed but preliminary tests suggest the entire water supply has been affected...